A joint replacement procedure is sometimes necessary to repair a joint having a diseased or damaged articulating surface. Such a procedure involves removal of the diseased or damaged portions of the joint and replacing them with a prosthetic implant. This is often a desirable procedure for ball-and-socket type joints, particularly the shoulder and hip joints. A shoulder joint replacement procedure, for example, often involves removal of the humeral head and replacement thereof with an implant including a stem and a head. It is important that the implant be positioned correctly within the joint in order to ensure that appropriate joint kinematics, including range of motion, are preserved so as to replicate, as closely as possible, those of the original joint.
The structure of prosthetic joint components has been developed to be suited for permanent implantation into the joint and includes features that may promote bony ingrowth, adhesion using cement, press-fit or a combination thereof. Particularly, in the case of implants including a stem, such as those used in shoulder arthroplasty, these features are included on the outside surface of the stem. Such features are not well-suited for use during the assessment of joint kinematics. Accordingly, instruments to be used in this part of the procedure have been developed. For shoulder arthroplasty, two general types of such devices have been developed, both of which are affixed to the bone during joint kinematic evaluation and removed therefrom after a proper position for the implant has been determined.
One such device is an externally-fixated jig. These devices, however tend to be bulky, complex and time consuming to set up and use. They also require the use of external fixation devices and/or power tools that introduce further complications to the surgical procedure. Because these devices exit through the incision to the outside of the body they are generally cumbersome, making accurate range of motion assessment difficult. Such jigs are shown in U.S. Pat. Nos. 6,267,785 and 6,193,758.
An additional or alternative device is a trial. Typically, these devices are designed to correspond to an implant in size and shape. The trial is designed to be temporarily inserted into a prepared medullary canal of the humerus in a manner similar to that of an implant. Known trials are typically used in conjunction with a lap sponge that is temporarily wrapped around the distal portion of the trial. The sponge-wrapped trial is then wedged into the canal, the sponge promoting a pressure fit therebetween, to evaluate the appropriate position for the implant. In the alternative, a foam ring can be assembled onto the trial stem as discussed in the brochure entitled Zimmer Trabecular Metal™ Humeral Stem Four-Part Fracture Surgical Technique, available from Zimmer, Inc., P.O. Box 708, 1800 West Center Street, Warsaw, Ind. 46581-0708. While eliminating the problems associated with externally-fixated devices, known trials present other problems. For example, by positioning a resilient material, such as a sponge, between the inside surface of the prepared medullary canal and the trial stem, the stem may be allowed to move within the joint leading to an unreliable joint kinematics assessment. Additionally, the use of a lap sponge to hold the trial within the medullary canal leads to a risk of leaving sponge or cloth debris behind in the bone after the trial is removed.
It is therefore necessary to provide a device that can be used for improved assessment of joint kinematics during a joint arthroplasty procedure conducted on a joint.